In order to improve the throughput, a MIMO-based communication method for transmitting and receiving signals through a plurality of antennas is considered in many communication systems.
If the transmission channel condition is known to the sender and the receiver in the MIMO system, it is possible to improve the throughput using the right transmission and reception filters designed for the right purpose.
In this case, all of the communication nodes have to know the information on the MIMO channels to process the signals so as to mitigate interference from adjacent nodes and remove the influence of multiple channels. In the MIMO communication system, unlike the downlink channels that are estimated using pilot signals without difficulty, the uplink channel estimation is not easy due to the necessity of channel information feedback and increases complexity of signal exchange.
Particularly in the MIMO system adopting a beamforming technique, the sender has to know the information on all MIMO channels and the increased signaling overhead boosts the complexity.
In order to reduce to hardware and signal processing complexity of the MIMO system, an antenna selection technique is effective but degrades the system throughput as compared to legacy MIMO systems using all of the antennas.
Typically, the performance of the conventional MIMO communication technologies (multiplexing gain and diversity gain) depend on the number of receive antennas and, although the number of transmit antennas is greater than that of the receive antennas, the number of symbols transmitted at a time is limited by the receive antennas. This means that the use of the transmit antennas greater in number than the receive antennas gives no extra gain.
Accordingly, the large number of transmit antennas in the MIMO communication system increases the implementation complexity. The aforementioned antenna selection technology has been proposed to keep the balance between the system performance and complexity through selective use of the antennas. However, the MIMO communication system based on the antenna selection system also has a drawback in that the increase of the number of antennas boosts the complexity abruptly and thus the overhead.